Phenylalanine Ammonia-Lyase GhPAL9 Confers Resistance to Verticillium Wilt in Cotton

Verticillium wilt (VW), induced by the soil-borne fungus <i>Verticillium dahliae</i>, represents a significant threat to global cotton production. Phenylalanine ammonia-lyase (PAL) is an essential enzyme in lignin metabolism that helps plants defend themselves against pathogenic fungal. Nonetheless, its role in imparting resistance to <i>V. dahliae</i> in cotton required further investigation. This study identified the <i>GhPAL9</i> (GH_D04G1247) as a crucial gene in cotton resistance to <i>V. dahliae</i> via RNA-seq analysis, demonstrating significant upregulation in the resistant variety Xinluzao84. Bioinformatics analysis revealed the conserved evolutionary relationship of GhPAL9 with PAL homologs across various species and highlighted stress-responsive cis-elements in its promoter region. The expression of <i>GhPAL9</i> was rapidly activated in roots, stems, and leaves following infection with <i>V. dahliae</i>, peaking between 2 and 8 h post inoculation (hpi). Silencing <i>GhPAL9</i> through virus-induced gene silencing (VIGS) technology intensified disease symptoms, elevated relative fungal biomass, and diminished lignin accumulation, thereby affirming its function in cotton resistance to <i>V. dahliae</i>. The overexpression of <i>GhPAL9</i> in <i>Arabidopsis</i> improved resistance to <i>V. dahliae</i>, and the OE-<i>GhPAL9</i> transgenic lines demonstrated reduced disease severity and diminished relative fungal biomass. The results gave us new information about how VW resistance at the molecular level, which established that <i>GhPAL9</i> acted as a positive regulator to increase resistance to VW via lignin accumulation.